1. Field of the Invention
This invention relates to devices for dispensing and mixing liquids, and more particularly to such devices that dispense and mix chemicals, and even more particularly to devices that dispense and mix cleaning chemicals.
2. Prior Art
It is common practice to purchase concentrated cleaning chemicals and to mix them with other liquids such as water to achieve the desired usage concentration for cleaning. A variety of proportioning dispensers have been developed to achieve this. The dispensers often employ venturi-type devices sometimes called eductors to draw the concentrated liquid chemical and mix it with the water stream. Examples of such eductors include the Sand U.S. Pat. Nos. 5,522,419, 5,253,677 5,159,958, and 5,862,829 all of which are assigned to the Assignee of the present invention and are expressly incorporated herein. Water traveling through the central, constricted portion of the venturi creates suction which draws the concentrated liquid chemical into the water stream.
The structure of such eductors is generally fixed, and thus, for a given water stream flow rate, the amount of concentrated liquid chemical drawn is a function of the fluid resistance in the flow path of the concentrated liquid chemical. Adjusting the amount of chemical educted is generally controlled by a metering orifice interposed into the flow path of the concentrated liquid chemical. Such orifices may be fixed or adjustable to vary the proportionate flow. Achieving the proper proportion of chemical merely with selection of a metering orifice is complicated by factors which vary per the application, such as the desired usage concentration, the viscosity of the concentrated liquid chemical, and the pressures at which the liquids are provided. Using metering orifices to control dilution means that very small metering orifice sizes are required, as shown in Table 1.
TABLE 1 Approximate Dilutions at 40 psi for Water-Thin Products (1.0 cp) Ratio (per Eductor Flow) Orifice Size (inch) Standard Drill Number 1 G.P.M. 3.5 G.P.M. 0.187 (3/16) 3:1 3.5:1 0.128 (30) 3:1 4:1 0.098 (40) 3:1 4:1 0.070 (50) 4:1 8:1 0.052 (55) 5:1 14:1 0.043 (57) 7:1 20:1 0.040 (60) 8:1 24:1 0.035 (65) 10:1 30:1 0.028 (70) 16:1 45:1 0.025 (72) 20:1 56:1 0.023 (74) 24:1 64:1 0.020 (76) 32:1 90:1 0.018 (77) 38:1 128:1 0.014 (79) 64:1 180:1 0.010 (87) 128:1 350:1
Metering orifices generally achieve dilution ratios of 2:1 to 300:1. More dilute mixtures are constrained by the volume rate of water available and by the smallest practical size of the metering orifices. Very small orifices are susceptible to clogging such as from contaminant particles or artifacts in the concentrated chemicals. In addition, the viscosity of the chemical imposes a size limitation. Introducing a fixed pressure drop to the overall dimensioning of the chemical feed line, or supply conduit, to achieve more dilute concentrations would preclude applications requiring less dilute concentrations.
Active devices which could monitor the relative amount of liquids being mixed and control dispensing are impractical as being uneconomical, increasing the cost of producing the dispenser. Moreover, providing such active devices with a power supply such as batteries or an electrical outlet is generally uneconomical or inconvenient. Moreover, dispensing devices often dispense conductive or corrosive materials that would further complicate protection of electronic components of an active system. Consequently, passive dispensing devices are generally used, even though this constrains the range of achievable usage concentrations.
Consequently, appropriate chemicals for dispensing are not concentrated as much as would be desirable, imposing additional costs of shipment. Dispensing devices for such less-concentrated liquid chemicals are thus required to have provisions for larger storage of chemicals and/or more frequent refills. In addition, at the more dilute end of the generally achievable range of operation, the metering orifice is susceptible to clogging, allowing defective mixtures to be generated. Moreover, certain types of chemicals that tend to have suspended solids are precluded from being dispensed at all by such devices.